1. Field of the Invention
The present invention relates generally to multiplex demodulators and specifically to FM stereo multiplex demodulators suitable for use with an FM stereo receiver.
2. Description of the Prior Art
In FM stereo broadcasting it is known to use the following, or similar, signal processing steps in order to demodulate a composite signal and to provide the left and right channel stereo audio signals. First, the composite signal is demodulated by a switching signal having the sub-carrier frequency, so that the composite signal is demodulated into left and right channel audio signals. Because of this demodulation technique these left and right channel signals have a crosstalk component, and this must then be cancelled from the demodulated audio signals. The last step is typically a deemphasis step which is carried out in order to bring the transmitted signals back to the correct level. The deemphasis is required becaused it is the general approach to emphasize the high-frequency end of the signal prior to transmission.
Nevertheless, while this known FM stereo multiplex demodulation technique is acceptable in some situations, if large amplitude operation is required when the power source voltage is low a large amount of unacceptable distortion will be present. Therefore, when the known FM stereo multiplex demodulator is operated by a battery, that is, a relatively low voltage power source, the signal level must be kept quite small, thereby resulting in obvious disadvantages in relation to the signal-to-noise ratio (S/N).